1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus. The invention relates more particularly to a technique for reducing cost and power consumption of a three-dimensional diagnostic apparatus by decreasing the number of delay circuits used for forming reception beams, in the three-dimensional diagnostic apparatus for obtaining a real-time three-dimensional image by three-dimensionally scanning a human body by applying ultrasonic beams thereto.
2. Description of the Background Art
(1) Two-dimensional ultrasonic diagnostic apparatus Conventionally, there has been known an ultrasonic diagnostic apparatus for obtaining a two-dimensional tomogram of a subject such as a human body.
FIG. 1 shows a part of a conventional two-dimensional ultrasonic diagnostic apparatus. This two-dimensional ultrasonic diagnostic apparatus employs a one-dimensional array probe 101 having a plurality of fine transducers 100 arranged in one row as shown in FIG. 1.
The operation of the two-dimensional ultrasonic diagnostic apparatus will be explained below.
At the time of transmitting ultrasonic beams from the two-dimensional ultrasonic diagnostic apparatus, a transmission electric signal is supplied to each transducer 100 through a delay circuit provided for each transducer 100. When each transducer 100 has received this transmission electric signal, each transducer 100 is driven, and ultrasonic beams are being sent from the transducer 100. By changing the delay time of each delay circuit, beam directions to a focus F of the ultrasonic beams can be changed as shown by solid lines and a dotted line in FIG. 1. The conventional two-dimensional ultrasonic diagnostic apparatus is structured to scan a subject by the ultrasonic beams in a desired direction by arbitrarily changing the delay time set in each delay circuit.
On the other hand, at the time of receiving ultrasonic beams in the two-dimensional ultrasonic diagnostic apparatus, each transducer 100 detects a reflection wave (echo) reflected from the focus F.
FIG. 2 shows a structure of the two-dimensional ultrasonic diagnostic apparatus. Each detection signal detected by the transducer 100 is delay processed with a predetermined delay time by a delay circuit 102 shown in FIG. 2. By this delay processing, phases of the detection signals corresponding to the focus F are matched. The detection signals after the phase matching are added together by an adder circuit 103 to be formed as a reception signal. This signal is then supplied to an image processing circuit. The image processing circuit executes a predetermined image processing to reception signals to reconstruct a two-dimensional tomogram and displays it in a display. With the above-described processing, it is possible to obtain a two-dimensional tomogram of a subject. The above-described two-dimensional ultrasonic diagnostic apparatus requires the delay circuits 102 by the number of the transducers 100 for simultaneously receiving reflection waves. These delay circuits are combined with the ultrasonic transducers to converge the ultrasonic beams into the focus F, and at the same time, controls the scanning direction of the ultrasonic beams and directivity of each transducer as a sensor.
Next, according to the conventional ultrasonic diagnostic apparatus, there has been put into practical use a so-called real-time display for displaying images obtained in real time from ultrasonic waves. To achieve this real-time display, it is necessary to display images of 10 to 30 frames every second. For reconstructing these large number of frame images, there is required information of a large number of scanning lines that comprise the frames. As one of methods for a real-time display, there is "parallel simultaneous reception processing". This parallel simultaneous reception processing is a method for obtaining information of a plurality of scanning lines in one-time transmission of ultrasonic wave. To be more specific, a plurality of scanning lines whose directivity mutually differ are set within the ultrasonic wave to be transmitted, and a plurality of reception signals along these scanning lines are formed, synthesized and signal-processed thereby so as to reconstruct ultrasonic tomographic images on the plurality of scanning lines.
FIG. 3 shows a structure of the two-dimensional ultrasonic diagnostic apparatus for carrying out the parallel simultaneous reception processing. Steps of the parallel simultaneous reception processing will be explained with reference to FIG. 3.
In the parallel simultaneous reception processing, a plurality of delay circuits 102 are provided in one reception channel 105 corresponding to one transducer 100 as shown in FIG. 3. By setting different delay times for these delay circuits 102, a plurality of detection signals with different phases are formed. Next, of the detection signals from the delay circuits 102 of the respective reception channels 105, detection signals of the same phase are added together by the adder circuit 103, so that a plurality of reception signals are formed. By reconstructing these reception signals, one ultrasonic tomographic image is obtained.
The above-described parallel simultaneous reception processing requires the delay circuits as follows:
the number of delay circuits=the number of the transducers.times.the number of parallel simultaneous receptions PA1 the number of delay circuits=the number of the transducers.times.the number of parallel simultaneous receptions
In this case, the number of ultrasonic transducers is equal to the number of reception channels. The number of parallel simultaneous receptions is equal to the number of scanning lines per one reception channel.
In general, the number of reception channels held by the two-dimensional ultrasonic diagnostic apparatus is about 100, while the number of parallel simultaneous reception is about four. Accordingly, the number of delay circuits required by the two-dimensional ultrasonic diagnostic apparatus is: EQU 100 channels.times.4=about 400
(2) Three-dimensional ultrasonic diagnostic apparatus
A three-dimensional ultrasonic diagnostic apparatus will be explained next. There has been an attention focussed on the three-dimensional ultrasonic diagnostic apparatus in recent years. The three-dimensional ultrasonic diagnostic apparatus employs a two-dimensional array probe having a plurality of rows of array probes, each row having a plurality of transducers arranged in one row. With this two-dimensional array probe structure, a subject is scanned three-dimensionally by applying ultrasonic beams to obtain a three-dimensional image of the subject. Since this three-dimensional ultrasonic diagnostic apparatus has the array probe arranged two-dimensionally, it is necessary to process detection signals output from in excess of 1000 transducers. At the same time, the number of scanning lines required becomes enormous for reconstructing a three-dimensional image by carrying out a three-dimensional scanning. Therefore, in the three-dimensional ultrasonic diagnostic apparatus, the above-described parallel simultaneous reception processing becomes inevitable for obtaining a plurality of scanning lines in one transmission, particularly in the case of carrying out a real-time display.
In this three-dimensional ultrasonic diagnostic apparatus, the number of delay circuits required for carrying out the above parallel simultaneous reception processing is obtained by the following formula, in a manner similar to that of the two-dimensional ultrasonic diagnostic apparatus:
To be more specific, in the three-dimensional scanning, the two-dimensional array probe structure requires thereception channels by the number of at least 32 channels.times.32 channels, for reducing the artifact to a practical level. In this case, the number of the parallel simultaneous receptions becomes 4.times.4. Accordingly, the three-dimensional ultrasonic diagnostic apparatus requires an enormous large number of delay circuits obtained by the following formula: EQU 32 channels.times.32 channels.times.4.times.4=16,384
Providing the above enormously large number of delay circuits in the three-dimensional ultrasonic diagnostic apparatus results in an increased manufacturing cost of the apparatus with an increase in power consumption and enlarging a scale of the apparatus.
As explained above, in the conventional three-dimensional ultrasonic diagnostic apparatus for carrying out a real-time display, there has been a problem of high manufacturing cost of the apparatus with large power consumption.